Hydraulic fluids and lubricating compositions



Patented Aug. 17, 1954 HYDRAULIC FLUIDS AND LUBRICATING COMPOSITIONSForrest J. Watson, Berkeley, Calif., assignor to ShellDevelopmentCompany, Emeryville, Califi, a corporation of Delaware No Drawing.Application October 27, 1951, "Serial No. 253,556

This invention is directed to lubricating compositions and hydraulicfluids having improved technical properties. More particularly, theinvention pertains to such compositions containing componentsimparting-improvedlow temperature properties, corrosion resistance andlow fiammability.

Current developments in aviation and industrial fields require the useof lubricants and hydraulic fluids having high resistance to corrosion,ilow flammability, and especially improved properties at the lowoperating temperatures which are encountered, for example, during theoperation of aircraft, and the like. Numerous proposals havebeen madefor correcting one or another of theseaproperties, but such correctionis usually .elfected .at the expense of another property of the fluids.For example, the use of aryl phosphates, such as tricresyl phosphate, asa hydraulic fluid is satisfactory only at moderate temperatures due tothe highsensitivity of .said phosphates to thermal influences. The arylphosphates, however, are beneficial in having great resistance toflammability. Heavy mineral oils may be used in similarsituations, butare of limited use under cold conditions due to their high pour points.Alkyl phosphates may be used under certain limited conditions .in anunmodified state, but are usually unsuitable for lubricating purposesand the like due to their-mediocre resistance to flammability and theirinherent low viscosity. Mixtures of lubricants have been suggested, butheretofore such combinations have been limited due, for example, "to therelatively lowrniscibility of aryl phosphates with mineral lubricatingoil's.

:"It is an object of the present invention to provide improvedlubricantsfor use at both low and high temperatures. It is another:object of this invention :to provide improved hydraulic fluids :andlubricating compositions combining in an optimum degree the propertiesof .high non-flammability and low response to thermal "changes. Otherobjects will become apparent during the following discussion.

Now in accordance with the present invention, it has been found that theaboveand other ob jects may be accomplished by combining high viscosityindex bright stock with normally liquid aliphatic phosphorus esters.More specifi- 6 Claims. (Cl. 252-75) cally, the compositions-ofthepresent invention comprise from about 7.5% to about by weight of ahighviscosity index bright stock and from about 40% to about 925% of analiphatic ester of a phosphorus acid,

THE COMPOSITIONS The compositions of this invention comprise two mainingredients as generally referred to above. In their preferredembodiments, the hydraulic fluids of this invention comprise from about30 to about 50% by Weight of a bright stock and from about 50% to aboutby weight of an aliphatic ester of a phosphorous acid. While thesecompositions are preferred for use as hydraulic fluids, somewhatdifierent mixtures are more suitable for use as aircraft turbo-prop orturbo-jet lubricants. The latter preferably contain from about 9 toabout 20% of bright stock and from about to about 91% of an aliphaticester of a phosphorus acid. In both types of compositions the preferredester is a tri-alkyl phosphate, which will be defined more fullyhereinafter. Optimum properties are obtained, however, if the tri-alkylester contains alkyl groups having at least 6 carbon atoms and usuallybetween about 6 and about 12 carbon atoms each, the total carbon atomcontent of each molecule thus being at least about 18 carbon atoms.

In addition to the two principal components which are the essentialfeatures of this invention, other ingredients may be added in order toprovide desirable properties. An especially effective type of additivefor the prevention of corrosion under oxidizing conditions in thisparticular mixture of liquids comprises the metallic salts ofcondensation products of formaldehyde with alkyl phenols; preferably thecalcium salt is employed. A synergistic effect has been found to occurin this composition when the latter additive is combined with anaromatic amine such as phenyl alpha naphthylamine. In addition, otherimportant additives finding use with certain of the subject compositionscompriseespecially pour point depressants such as the polymerized estersof the acrylic acid series and the like, especially aliphatic esters ofpolymerized methacrylic acid.

BRIGHT STOCK While the present invention is not to be confinedto the useof a mineral oil derived from any particular source or by any particularrefining process, the usual source of suitable mineral oils comprisesthe fraction thereof generally termed bright stocks, and particularlybright stocks having a viscosity index of at least 60. The term brightstock is one which is well recognized in the art of refining mineraloils. To obtain the desired fraction, crude oils are usually subjectedto distillation under ordinary pressures in order to obtain a longresidue comprising the fraction which does not distill under theseconditions without substantial decomposition. The long residue is thensubjected to steam distillation,

usually under a vacuum. Under these conditions,

gas oil and waxy lubricant fractions distill over, leaving what isnormally termed a short residue or a steam refined stock, also known ascylinder stock. The steam refined stock is then deasphalted (if anasphaltic crude is employed) and subjected to dewaxing operations toremove microcrystalline or macrocrystalline waxes. Following this, therafiinate is treated with a solvent for the purpose of reducing orremoving the aromatic fractions. Clay contact treatment or percolationmay be employed to clean up the oil following any one or all of theseseparate operations. The rafiinate which remains after deasphalting,dewaxing, extraction, and clay treatment is generally called brightstock.

The bright stocks suitable for use in the present compositions shouldhave the following ranges of properties:

Table I PROPERTIES OF BRIGHT STOCKS Viscosity, S. U. S,, 100 F. 1250,usually 125011,000,

preferably 1500-3500 Viscosity, S. U. 8., 210 F. 75, usually 125-325,preferably 150-250 Viscosity index +60, preferably +85-110 Anilinepoint, C. 100, preferably 115 Flash, F. 475, preferably 500 Fire, F.550, preferably 600 Pour point, F.maximum 25, preferably lower than 15Percent aromatics 15, preferably 10 opt. 5

Percent naphthenes 35 Percent paraffines, at least 60 The tables whichfollow give :the properties of typical bright stocks which are useful inthe compositions of this invention.

4 vention is predicated upon the use of a mineral oil fraction havingthe above defined ranges of properties and not upon the source ortreatment of such oil. I

The two most important inherent properties of a mineral oil suitable forthe present use comprise the aromatic content and the viscositycharacteristics. The aromatic content has a large influence upon thesensitivity of the oil to thermal changes and the viscosity of the oilsdefines their suitability for their present purpose. Hence, the bestdefinition with respect to essential characteristics of mineral oilsuitable for the present compositions comprises those having an aromatichydrocarbon content less than about 15% by weight and having a viscosityof between about 1250 and about 11,000 SUS at 100 F. Having definedthese particular properties, the other properties such as flash, fire,aniline point, and viscosity index usually, are largely dependent uponthem.

THE PHOSPI-IORUS ESTERS The phosphorus esters useful for inclusion inthe present compositions comprise the normally liquid aliphatic estersof acids of phosphorus.

While the trialkyl phosphates are particularly preferred, other classesare suitable in addition to or in place of said phosphates. Theseinclude dialkyl hydrocarbon phosphonates, especially dialkylalkanephosphonates, alkyl dialkanephosphinates, diphosphorus compoundssuch as bis (dialkyl phosphono)alkanes, bis(alky1 alkane phosphino)alkanes, alkane diol bis(dialkane phosphinate), alkane diol bis(dialkylphosphates), alkane diol bis(alky1 alkane phosphonates) and thecorresponding ethers of the above diphos- Table II EXAMPLES OF TYPICALBRIGHT STOCKS SUS Ring Analysis Ratio of Viscos- Paraf- Average Averagefines to Mol Rings per 100 210 Index Aro- Naph- Paraf- Naph- Weight Molmatic thenes fines thenes Mid-Continent Bright Stock-ConvcntionalExtraction 3, 650 164 77 13 17 4. 1 685 3. 7 M1d-Oont nent BrightStock-Mild Extraction 2, 569 141 9 19 72 3. 8 685 3. 4 Mid-ContinentBright StockHeavy Extractlon 2, 049 131 93 3 21 76 3. 62 675 2. 9Pennsylvania Bright Stock... 2, 109 144 102 5 16 79 4. 730 3. 0 CoastalBright Stock 1, 251 85 63 4 35 61 1. 74 515 3- 4 Table IIISPECIFICATIONS FOR TYPICAL MID-CONTINENT BRIGHT STOCKS UnfilteredFiltered 24.5 25. 5 Dark Green. (3. 7

l0. 10 545 610 -150 Viscosity Index, minimum- 90 mg, clay treating, acidtreating, and the like. 75

Hence, it will be recognized that the present in phorus compounds.Classes of the latter which are included are bis(dialkyl phosphonoalkyl) ethers, bis(alkyl alkanephosphinico alkyl)ethers and bis(dialkylphosphato alkyl) ether.

The phosphorus esters which are particularly useful in thesecompositions ordinarily have a total of at least 18 carbon atoms permolecule; preferably this total is between about 20 and about 32 carbonatoms per molecule. Typical trialkyl phosphates which are especiallysuitable contain alkyl radicals having from about 6 to about 12 carbonatoms each and include the following:

Trihexyl phosphates Triheptyl phosphates Tricotyl phosphates, e. g.,

Tri(2-ethylhexyl) phosphate OR Tri (isooctyl) phosphate Trinonylphosphates, e. g.,

Tri (3,5,5-trimethylhexyl) phosphate Tridecyl phosphates Tridodecylphosphates pihexyl octyl phosphate aeeaveo 5,. Typical species ofphosphonates and phosphinates are given below:

Dialkyl hydrocarbon phosphonates:

Di( 2-ethylhexyl) hexanephosphonate Dihexyl hexanephosphonate lDioctyl(3,5,5 trimethylhexane) phosphonate Dihexyl benzenephosphonateA-lkyl dialkane phosphinates:

Butyl di(2-ethylhexane) phosphinate Hexyl diheptane phosphinatesReferring now to the diphosphorus compounds, these may be representedwith the following general formula:

wherein each R is an aliphatic hydrocarbon radical.

The above classification of diphosphorus compounds includes especiallysubstituted aliphatic hydrocarbons bearing 2 phosphorus radicals in theform of phosphate, phosphonate, phosphinate, or phosphine oxide groups.One of the more preferred classes of liquids suitable for use, accordingto the present invention, includes the bis(dialkyl phosphono)a1kanes.These have the general configuration of Preferably R1 in the aboveformula is an alpha, omega-alkylene hydrocarbon radical of at least 3carbon atoms. Each of the other R substituents may be a hydrocarbonradical of such nature that the entire compound is substantially fluidat operating temperatures. Preferably each of these groups contains from3 to 9 carbon atoms each, and still more preferably at least two of themare of branched configuration. The following suitable species aretypical of this presented configuration:

Bis-1,3-(diisobuty1 phosphono) propane Bis-1,4+ (diisopropyl phosphono)butane Bis- 1,5- [di (B-methylbutyl) phosphonol pentane Bis-1,6-[di(2-ethy1hexyl) phosphonol hexane Bis-1,3- [di(3,5,5-trimethylhexyl)phosphonolpropane The alkylene group separating the two phosphorusradicals may be shorter than about 12 carbon atoms or may be of branchedconfiguration as typified by the following species:

Bis-1,2-(di-tert-butyl phosphono) ethane Bis-1,2- (di-tert-butylphosphono) -3,l-dimethylpentane Bis-2,5l- (di-sec.-buty1 phosphono)-3,5-dimethylhexane Bis-1,6- (di-n-pentylphosphono)-3,4,5-trimethylhexane Another suitable subgeneric group of phosphoruscompounds useful in the practice of this invention comprises thealkanediol bis(dialkane phosphinates). These materials have the generalconfiguration:

The preferred configurations and carbon contents of the individualportions of this and the following classes are in general those given inthe foregoing description of the bis dialky1 phosphono alkanes exceptwhere especially noted. Preferably the substituent R1 contains from 3 to9 carbon atoms while the remaining Rs have from i to 9 carbon atomseach. The following species are typical of this class:

1,5-pentanediol bis- [di (2-ethylhexane) phosphinate] 1,6-hexanedio1bis- [di (2-isobutane) phosphinate] L'I-heptanediolbis-(di-n-butanephosphinate) 3,4-heptanediol bis-[di(3,5,5trimethylhexane) phosphinate] 2,5-hexanediol bis-(dipentanephosphinate)l Another class of compounds coming within the general scope of thisinvention are the tetraalkylalkylenediphosphine oxides. These materialshave the following general formula:

Ihe following species are typical of this class of compounds:

The following list of suitable species illustrates this group:

1,6-hexanediol bis(dibutyl phosphate) 3-methyl1,6-hexanediolbis(di-tert-butyl phosphate) 2,3-diethyl-1,6-hexanediol bis(di-sec-amylphosphate) 2,4,e-trimethyl 1,5-pentanediol bis(di-3,5,5 trimethylhexylphosphate) 1,4-butanediol bis(diisopropyl phosphate) Another sub-genericclass constitutes alkanediol bis alkyl alkanephosphonates) which havethe general configuration:

The suitable species which follow illustrate the nature of this class:

1,5-pentanediol bis-(butyl butanephosphonate) 1,4-butanediolbis-(tert-butyl 2-methyl-1-pro- .panephosphonate) l,6-hexanediolbis-(3,5,5-trimethylhexyl butanephosphonate) 3,l-dimethyl-1,6-hexanediol bis-(tert-amyl pentanephosphonate)1,2-ethanediol bis-(3,5,5-trimethylhexyl butane- .phosphonate) l Anotherclass of compounds to be considered includes bis-(alkylalkanephosphinico)alkanes which have the general configuration:

This class is exemplified by the following species:

It will be understood that symmetrical compounds are not necessary forthe operation of the present invention. For example, the varioussubstituents denoted as R in the above general formulae may vary withina given compound,

both with respect to carbon atom content and to spatial configuration.The branched configurations are favored due to their generally superioreffect upon the lubricating characteristics, especially at lowtemperatures. Unsaturated hydrocarbon radicals are especially to bedesired when they are directly attached to a phosphorus atom since theirpresence has been found to improve the corrosion characteristics oflubricants prepared therefrom. Additionally, while the two end groupsmay be identical in a single compound for specific purposes, it issometimes desirable to include two different types of phosphorus endgroups in order to obtain the beneficial properties attributable to eachtype. Suitable illustrating compounds having mixed end groups are asfollows:

l (butyl butanephosphinico) 2 (di secbutyl phosphono)ethane l (di 2ethylhexanephosphinate) 5 (dibutyl phosphate) pentanediol Typicalspecies of the corresponding ethers of di-phosphorus compounds are thefollowing:

Bis-E di-amylphosphono) methyl] ether Bis-E (di-laurylphosphono) ethyl]ether Bis- (butyl hexanephosphinico) ethyl] ether Bis-E (di-isopropylphosphono) amyll ether Details of the preparation and properties ofthese and other ethers will be found in copending application Serial No.214,432 filed March 7, 1951, by Denham Harman et al.

The above classes of compounds may be prepared by the following typicalmethods:

The preparation of bis-(dialkyl phosphono)- alkanes illustrates theconditions necessary for the preparation of typical compounds. In thisparticular instance sodium is suspended in a suitable solvent (such asrefluxing heptane) after which a dialkyl phosphite is added and refluxedfor a period of 1 to 4 hours to form a sodium dialkyl phosphite.Subsequently a dibromoalkane is gradually added to the refluxingsolution. After heating for 1 to 8 hours at reflux, the correspondingbis-(dialkyl phosphono) alkane has been formed. Sodium bromide isfiltered off and the remaining solution is water Washed, neu tralizedwith dilute alkali, water-washed again and the volatile diluent isremoved by topping to a temperature of about 150 C. at 150 mm. pressure.If a highly purified product is desired the bottoms from this toppingoperation may then be distilled in a molecular still to obtain apurified product as distillate.

The preparation of alkanediol bis-(dialkyl phosphate) is preferablyeffected by reaction of an alkylene glycol with a dialkylchlorophosphate in the presence of a hydrogen chloride acceptor.Preferably the components are added to one another at a temperaturebetween about 10 C. and +20 C. and then warmed on a steam bath for aperiod of time between about 1 hour and 16 hours, preferably between 2and 4 hours. Typical hydrogen chloride acceptors are amines, such astrimethylamine, pyridine, or dimethylaniline. Alternatively, thehydrogen chloride evolved during the reaction may be removed as it isformed by a current of air. Followin the reaction, the mixture iswater-washed to remove hydrochloride salts or the salts (such aspyridine hydrochloride) may be removed by filtration. The mixture isthenwashed with dilute hydrochloric acid to remove any excess base which maybe present. Purification may be completed by distillation of thevolatile constituents leaving the desired phosphate compounds.

In the preparation of the tetra-alkylalkylenediphosphine oxides, thefollowing conditions have been found to be suitable: A tetra-alkyldiphosphonoalkane is treated with phosphorus pentachloride at atemperature between 75 and C. for a period of time, preferably between 2and i hours. The product of this reaction is atetrachlorodiphosphonoalkane. This product is then treated with aGrignard reagent (an organo magnesium halide) at a temperature between 0and 25 C; for a period of 2 to 4 hours. The resulting product is thedesired bis-phosphine oxide.

A suitable preparation for bis-(alkyl alkanephosphinico)alkanescomprises treatment of a dialkyl alkanephosphonite with a dibromoalkaneunder the conditions of the well-known Arbuzov reaction.

One property of this general class of diphosphorus derivativesdistinguishing them from the more commonly employed monophosphates, suchas trioctyl phosphate, is their exceptional behavior with respect tocorrosion. These materials have been found to be substantiallynoncorrosive with respect to copper, magnesium, iron, cadimium, oraluminum. As a class, the diphosphorus compounds described hereinbeforehave suitable properties for use as hydraulic fluids. In general, theirviscosities are between 10 and 25 centistokes at about room temerature.The derivatives bearin 4 alkane to 2 phosphorus linkages or 2 alkane tol phosphorus linkages have substantially higher viscosities making themespecially suitable as synthetic lubricating 011s. The latter compoundsinclude especially alkanediol bis- (dialkanephosphinate) The followingtable illustrates the unexpected properties of a typical compositioncoming within the definition of the present invention:

Table IV PROPE RTIES Trioctyl Phosphate Percent 100 Bright Stock,Percent 100 Viscosity Index" 90 98 Pour Point, F 80 +27 -50Flammability- 14 l7 acea'zeo This, table shows, that anunexpecteduresult wasobtained inthe changes in three. properties.

resulting. from a the combination of trioctyl phosphate with a typical.brig-ht stock. In the first place, the viscosity index, of the blend is.about 50% higher than the viscosity indexof either of the components.The reasonfor this is obscure,

. sequently a base such aslime may be added and but constitutes anunexpected and beneficial result adding substantially to thevalue ofthis.

combinationof fluids. Secondly, it will be found fromthe above data thatthe pour point of the low that of the higher pqur point of one of the.

components. Hence, it was unexpected to discover that in this particularcombination the resulting pour pointof the blend was in fact 77 F. lowerthan that of the component having the higher pour point. Finally, thistable shows an unexpected feature with respect to flammability. Whilethis term is dependent upon the exact physical conditions under whichthe fluid is to be used, a testcalled the Pipe Cleaner Flammability Testhas been devised for differentiating between fluids under standardconditions for this property. Under the conditions which will bedescribed hereinafter, the addition of bright stock to .tri-octylphosphate actually reduced flammability instead of increasing it aswould normally be. expected. In other words, the addition of amineraloil (which is normally regarded as relatively flammable) reducedthe flammability of a phosphate estenwhich is normally regardedasrelatively non-flammable. Hence, the present invention is particularlypredicated upon the unexpected findings in these three properties,namely, with respect to viscosity in:

dex improvement, blended pour point advantage and reduction infiammability.

METALLIC SALTS Insome applications the compositions as definedhereinbefore cause corrosion of certain metals, and under oxidizinginfluences exhibit an increase in viscosity under operating conditions.Itwas found that only certain specific classes of additives could be.eifectively used in correcting these phenomena. The most eifectiveadditive for the purpose comprises the metallic salts of condensationproducts of formaldehyde with alkyl phenols. While the preferred metalin this respect is calcium, other effective metals are alkaline earthmetals such as barium and magnesium. These may be supplemented by heavymetal salts and alkali metal salts of the subject condensation productssuch as zinc, aluminum, copper, lead, iron, nickel, cobalt, manganese,chromium, tin, sodium, potassium and lithium.

The alkyl phenols are preferably thosehaving used. Underthese conditionsan efiective reducheating continued for a similarlength of time inordrto formthe metallic salt. Alternatively the salt may, be formedSimultaneously with condensation by utilizing the, metallic base as thecondensation catalyst. Preferably mineral oil is also present so thatthe resulting product is obtained in the form of an oil concentrateready for addition to liquid compositions. Further details of this typeof roduc are to be found in U. S. Patent 2,250,188 issued July 22, 1941,170

Chester E. Wilson.

In improving the compositions of this invention by the useof such salts,amounts between about 0.25% and about 5% by weight may be tion inmetallic corrosion may be obtained. The

following table illustrates the properties of a typatleast one alkylgroup with from 4 to 12 carbon atoms. The most effective members for thepresent purpose are tertiary alkyl phenols having from about 5 to about9. carbon atoms per alkyl radical. The condensation product formedbetween these alkyl phenols and formaldehyde are enerally prepared byheatingone Incl of the phenol with between about 7 and one molofformaldehyde with a catalytic amount of an acid or base. Normally thesemetals are heated for pericd l e w n' about on andt r e our at atemperature between about 175 and 225 F. S ubicai composition containingabout 1.0% of a calcium salt of the condensation product formed betweenformaldehyde and amyl phenol.

Table V Oxidation corrosion test, 16s hr. at 250 F'.--wt.

loss, mg /cmi Cu 0.03 Mg 0.02 Fe 0.02 Cd 3.81 1 0.01 Per cent increasein viscosity at 100 F. AcidNeut. No. after use 15.9 4 ball. wear (7 kg.,C.) 0.21 Pipe cleaner flash 17 Pipe cleaner fire. 21

AROMATIC AMINES Table VI Trioctylphosphate, wt. percent 59. 8 BrightStock, wt. percent 38. 2 Calcium Salt, Wt. percent 1 0 Phenyl alphanephthylamine, wt. percent Viscosity Cs. F Viscosity Cs. 210 F ViscosityIndex Pour Point, F Acid Neut. N o MILO5606 Specification-OxidationCarrosion Percent Increase in Viscosity at 100 F Acid Neut. No. afteruse diamine. The alkylated phenyl amines are also useful such asl-isopropyli-amino benzene, 1- hexyl 3 amino benzene, l amino 2 methyl-G-ethylbenzene and 1-amino-ZA-diethylbenzene.

In order to provide an effective synergistic result with the metallicsalts described hereinbefore, the aromatic amines should be present inan amount between about 0.25 and about 5% by weight of the totalcomposition. In the absence of the metallic salts described above, thearomatic amines have proved to be unsatisfactory for the purpose ofstabilizing these compositions against oxidation corrosion. On the otherhand, as described above, the metallic salts do not fully protectcadmium against corrosion and permit a substantial increase in viscosityupon exposure to oxygen. However, as the data contained in Table VIindicate, combinations of these two additives provide substantiallycomplete protection in these respects.

The pipe cleaner flammability test is made as follows: A pipe cleaner,reduced to 4 inches in length, is saturated with fluid to be tested, theexcess drained and the cleaner inserted in a metal holder. It is thencycled at 36 R. P. M. between two electric hot plates mountedhorizontally one-half inch apart with ceramic grids over the open coilheaters. The temperature between the grids varies between 760 and 710C., dropping during the test. The number of passes necessary to causeinitial flash and continuous fire are recorded.

In addition to the ingredients described hereinbefore, thesecompositions may contain other lubricating oil and hydraulic fluidcomponents or additives. In certain compositions wherein the proportionof bright stock is above about 35% and the composition is to be used atrelatively low temperatures, it is desirableto incorporate therein oneor more pour point depressants. The

most satisfactory type of material comprises polymerized esters of theacrylic acid series. These include especially the esters of methacrylicacid and of acrylic acid. The former are available as commercialproducts and are sold under the trade name Acryloid. The esters to beused should have molecular weights from about 5,000

to about 25,000, which will be understood to be an average figure forthe mixture of polymers normally present. The acids are esterified withaliphatic alcohols having from 2 to carbon atoms and the polymers may behomopolymers of a single ester or may be copolymers of a mixture of suchesters. The term polymerized esters will be understood to include bothof these types.

Another type of pour pointdepressant suitable for use in the presentcompositions includes the condensation products of high molecular weightparafiins and polycyclic aromatics such as the condensation productsproduced by condensing chlorinated paraffin wax and naphthalene.

I claim as my invention:

1. A composition comprising essentially from about 50% to about 92.5% byweight or a; normally liquid trialkyl phosphate said ester having atleast 18 carbon atoms per molecule, from about 7.5% to about 60% byweight of a mineral oil bright stock having a viscosity of between about1250 and 11,000 SUS at F., said oil containing less than about 15% byweight of aromatic hydrocarbons and said composition containing fromabout 0.25% to about 5% by weight of an alkaline earth metal salt of acondensation product of formaldehyde with alkyl phenols the alkyl groupsthereof containing from 4 to 12 carbon atoms, and 0.25-5% by weight of anaphthylamine.

2. A hydraulic fluid composition comprising the following ingredients inthe stated proportions:

Per cent.

Trioctylphosphate 59.8:

Mineral oil bright stock 38.2:

Phenyl alpha-naphthylamine 1. Calcium salt of the condensation productof formaldehyde with amyl phenol 1 Trioctyl phosphate 50-70 Mineral oilbright stock 30-50 Phenyl alpha naphthylamine 0.25-5

Calcium salt of the condensation product of formaldehyde with amylphenol 0.25-5

said mineral oil bright stock having a viscosity of between about 1250and 1,000 SUS at 100 F. and containing less than about 15% by weight ofaromatic hydrocarbons.

4. A hydraulic fluid composition comprising essentially the followingingredients in the stated proportions:

Per cent by weight Trialkyl phosphate, each alkyl radical thereofcontaining from 6 to 12 carbon atoms 50-70 Mineral oil bright stock30-50 Phenyl alpha naphthylamine 0.25-5

Calcium salt of the condensation product of formaldehyde with amylphenol 0.25-5

said mineral oil bright stock having a viscosity of between about 1250and 1,000 SUS at 100 F.

and containing less than about 15% by weight.

of aromatic hydrocarbons.

5. A hydraulic fluid composition comprising essentially the followingingredients in the stated proportions:

Per cent by weight Trialkyl phosphate, each alkyl radical thereofcontaining from 6 to 12 carbon atoms 50-70 Mineral oil bright stock30-50 A naphthylamine 0.25-5 Calcium salt of the condensation product offormaldehyde with amyl phenol 0.25-5

said mineral oil bright stock having a viscosity of between about 1250and 11,000 SUS at 100 F. and

omatic hydrocarbons.

Per cent by weight Trialkyl phosphate, each alkyl radical thereofcontaining from 6 to 12 carbon atoms 50-70 Mineral oil bright stock30-50 Phenyl alpha naphthylamine 0.25-5

Calcium salt of the condensation product of formaldehyde with alkylphenol, each alkyl radical thereof containing from 4 to 12 carbon atoms025-5 said mineral oil bright stock having a viscosity of between about1250 and 11,000 SUS at 100 F. and containing less than about 15% byweight of aromatic hydrocarbons.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,175,877 Clark Oct. 10, 1939 2,251,531 Wiezevich May 13, 19412,250,188 Wilson July 22, 1941 2,397,380 Smith et a1 Mar. 26, 19462,509,620 Watson et a1 May 30, 1950

1. A COMPOSITION COMPRISING ESSENTIALLY FROM ABOUT 50% TO ABOUT 92.5% BYWEIGHT OF A NORMALLY LIQUID TRIALKYL PHOSPHATE SAID ESTER HAVING ATLEAST 18 CARBON ATOMS PER MOLECULE, FROM ABOUT 7.5% TO ABOUT 60% BYWEIGHT OF A MINERAL OIL BRIGHT STOCK HAVING A VISCOSITY OF BETWEEN ABOUT1250 AND 11,000 SUS AT 100* F., SAID OIL CONTAINING LESS THAN ABOUT 15%BY WEIGHT OF AROMATIC HYDROCARBONS AND SAID COMPOSITION CONTAINING FROMABOUT 0.25% TO ABOUT 5% BY WEIGHT OF AN ALKALINE EARTH METAL SALT OF ACONDENSATION PRODUCT OF FORMALDEHYDE WITH ALKYL PHENOLS THE ALKYL GROUPSTHEREOF CONTAINING FROM 4 TO 12 CARBON ATOMS, AND 0.25-5% BY WEIGHT OF ANAPHTHYLAMINE.